This invention relates to an acoustic tool break detection method and system having an automatic gain control to adjust the cutting vibration signal to an average level, and especially to detection via AGC features of tool breaks that cause the cutting vibration signal level to slowly decrease.
A Machine Tool Monitor in a given installation has a cutting noise signal level that can vary widely due to such factors as workpiece material properties, depth of cut, surface speed, feed rate and rake angle. One current system relies on the part programmer to control the gain of the MTM analog signal channel between cuts so that the signal level remains in the general vicinity of the level that tests have shown optimizes tool break detection performance. The digital processor has signal pattern recognition logic to test for characteristic tool break acoustic signatures.
To reduce the burden on the part programmer, and to permit gain control during each cut, an AGC capability has been developed for the Machine Tool Monitor. A software digital automatic gain control is disclosed in copending application Ser. No. 027,367, filed Mar. 18, 1987, B. A. Green, Jr., and a hardware AGC circuit is in Ser. No. 943,397, filed Dec. 19, 1986, now U.S. Pat. No. 4,764,760, J. F. Bedard and W. Whipple. The latter teaches that the AGC time constant is made long enough, such as greater than 3 seconds, so that the rapid substantial changes in vibration signal level due to abruptly occurring tool fracture events, major enough to cause damage or force a recut, are not affected and these acoustic signatures can still be recognized by the tool break detection logic. However, as seen in FIG. 2, there is another type of tool break acoustic signature. The gradual signal level changes produced by a rapidly wearing tool or a crumbly break, which occur over a period of several seconds, are essentially removed by the AGC action if the input signal decreases steadily without abrupt drops. Consequently, no possible tool break detection logic applied to the AGC-modified signal could be successful in this case. Other crumbly type break events reduce the input signal level in a series of unevenly spaced abrupt but small drops no one of which meets the standard tool break detection logic requirements. This invention detects both variations of major tool break events that occur over a period of time rather than suddenly
The following are directed to tool break detectors in MTM systems that do not have an analog channel automatic gain control and alarm on detecting the more gradually occurring tool breakage: U.S. Pat. No. 4,642,617, the disclosure of which is incorporated herein by reference and application Ser. No. 835,698, filed Mar. 3, 1986, now U.S. Pat. No. 4,707,688 C. E. Thomas.
U.S. Pat. No. 4,514,797 is relevant and has a software-controlled automatic gain control in a worn cutting tool detector.